fiber width tracing and quick aperture corrections

[ajmejia]

Improved fiber width tracing in function imageMethod.trace_fiber_fwhm by fitting a Gaussian profile to each fiber. Main changes are:

• the fiber width tracing allows for variable width along cross-dispersion direction
• along with the FWHM of the fibers, the peak flux (or count rates) and the centroid are also traced
• improved fitting stability by fitting fibers in blocks along one column
• implemented continuum exposure modelling and comparison with observations
• implemented quick aperture corrections
• improved masked pixels handling in fiber fitting extraction
• applying aperture corrections in quick reduction